In numerous contexts a skew or misaligned article traveling on a track or conveyor can be troublesome for downstream machinery. Sorters, stackers, trimmers, and encoders are just a few examples of downstream machinery conventionally designed to accept articles only in axial alignment with the track. Restricted by this limitation, these devices are susceptible to erratic jamming precipitated by skewed articles. Unfortunately, jammed machinery necessitates inopportune down time and, in severe cases, costly repair.
A skew article can inflict damage not only to equipment, but to itself as well. Downstream machinery may "chew up" articles bent on skew suicidal courses down a conveyor. When destruction of nonfungible articles occurs, it can be difficult to ascertain the unique features of the obliterated articles and, consequently, to replace them in natural sequence.
Several skew detection systems attempting to avert the above consequences are currently available. Some of these systems are photoelectric. For example, U.S. Pat. No. 3,131,931 to Fechkowsky discloses a system which, in several locations, used two photoelectric cells to test whether a sheet is properly aligned with a registration bar. Thus, the registration bar itself forms a guide or standard for alignment and thereby impedes the travel of the sheet.
U.S. Pat. No. 3,240,487 to Templeton purports not to require conventional sheet registering bars or retractable sheet registering gates. Templeton employs a pair of horizontally spaced-apart photoelectric cells mounted on a guideway structure and illuminated by light beams. Unless the leading edge of a sheet blocks out both light beams, sheet registering rollers will reject the sheet. In this event, another roller repeatedly attempts to correctively realign the sheet. Importantly, when one of Templeton's light sources does prove faulty, a skewed sheet may pass through undetected. Thus, a disadvantage of the prior art is that when a light source malfunctions, a skew article may pass through undetected and proceed to jam machinery.
An envisioned exemplary but non-exclusive usage of this invention concerns document sorting and stacking, particularly mail sorting and stacking. Commonly assigned U.S. application Ser. No. 859,074 is illustrative of such an applicable environment. That particular system provides a document sorter which accepts coded location signals and automatically sorts the documents using a plurality of stackers. In such a system, a document which is in a skew position on an infeed conveyor causes complications at the stackers.
In light of the above problems, it is an object of this invention to provide a skew detection mechanism for checking both the alignment of articles traveling on a track or conveyor and the conditions of light sources.
It follows, therefore, that another object of this invention is to provide a skew detection mechanism which will not incorrectly indicate proper article alignment when a light source malfunctions.
Moreover it is an additional object of this invention to provide a skew detection mechanism which will reduce costly mechanical repairs and machinery down time caused by the jamming of skew articles in machinery.